Shifts in subjective well-being scales?

TL;DR Evidence suggests there aren't shifts in SWB scales over time. This topic isn't well understood. I've got a paper on this area in the works.

The question you're asking here - do individuals rescale, that is, alter what the end-points of their scales refer to? - is one component of a broader concern.

The broader question is whether subjective scales, those where individuals give numerical ratings of subjective phenomena are cardinally comparable, that is, whether a one-point change, on a given scale, represents the same size change in subjective experience for different people and at different times. For instance, if I say my happiness has gone from a 4 to an 5 out of 10, and you say your happiness have gone from a 3 to 4, can we conclude we each had the same increase in happiness?

Given how fundamental the concern is - it applies to all subjective data, not just SWB data - I've been surprised to find the topic hasn't been looked into a great deal. Two leading SWB researchers, Stone and Krueger, said this in an 2018 review article

one of the most important issues inadequately addressed by current [SWB] research is that of systematic differences in question interpretation and response styles between population groups. Is there conclusive evidence that this is a problem? And, if so, are there ways to adjust for it? Information is needed about which types of group comparisons are affected, about the magnitude of the problem, and about the psychological mechanisms underlying these systematic differences

I've been looking at the cardinality of subjective scales. I've got a working paper that I'm not quite ready to put online - this should only be another couple of months. The paper is an evolution of work I had in my DPhil thesis (pp. 135), where I broke cardinal comparability into a number of components, reviewed the evidence for each, and concluded SWB data probably best interpreted as cardinally comparable.

The topic is pretty complicated and addressing all of it would take too long here. I'll just provide a 'quick and dirty' answer to the specific concern you raise about rescaling (aka 'intertemporal cardinality'). Prati and Senik (2020) compare remembered SWB—how satisfied individuals recall being—with observed past SWB—how satisfied individuals they said they were at the time. The use a German panel data where individuals were given 9 different pictures of changes in life satisfaction over time (e.g. staying flat, going up, going up then going down, etc) and asked to pick the one that best represented their own life.

There turns out be an (I think) pretty amazing match between the patterns of observed past and remembered SWB. This is only possible if either (A) individuals both use the same scale over time and have good memories or (B) individuals change the scale use and have bad memories. If individuals used the same scales and had bad memories, or used different scales and had good memories, there would be an inconsistency between the recalled and past observed patterns. Of the two options, (A) seems far more probable than (B). It's hard to believe individuals really can't remember how their lives have gone. Further, we might expect individuals will try not to rescale so that their answers are comparable over time.*

Hence, there doesn't seem to be rescaling at the population level. Further research into whether there are some individuals who rescale, and what causes this to happen, would be good. I'm not aware of any.

*In fact, (B) requires quite specific and implausible patterns of memory failure. To illustrate, suppose your experienced satisfaction has been flat but, because your scale has been shrinking, your reported 0-10 level of satisfaction had been rising over time. To make your observed past satisfaction and your recalled satisfaction consistent, given this scale shrinkage, you would need to falsely recall that your satisfaction has increased. If you instead erroneously recalled that your satisfaction had decreased, then there would be an inconsistency between observation and recall.

I don't know, but I get the impression that SWB questions are susceptible to framing effects in general: for example, Biswas-Diener & Diener (2001) found that when people in Calcutta were asked for their life satisfaction in general, and also for their satisfaction in 12 subdomains (material resources, friendship, morality, intelligence, food, romantic relationship, family, physical appearance, self, income, housing, and social life), they gave on average a slightly negative rating for the global satisfaction, while also giving positive ratings for all the subdomains. (This result was replicated at least by Cox 2011 in Nicaragua.)

Biswas-Diener & Diener 2001 (scale of 1-3):

The mean score for the three groups on global life satisfaction was 1.93 (on the negative side just under the neutral point of 2). [...] The mean ratings for all twelve ratings of domain satisfaction fell on the positive (satisfied) side, with morality being the highest (2.58) and the lowest being satisfaction with income (2.12).

Cox 2011 (scale of 1-7):

The sample level mean on global life satisfaction was 3.8 (SD = 1.7). Four is the mid-point of the scale and has been interpreted as a neutral score. Thus this sample had an overall mean just below neutral. [...] The specific domain satisfactions (housing, family, income, physical appearance, intelligence, friends, romantic relationships, morality, and food) have means ranging from 3.9 to 5.8, and a total mean of 4.9. Thus all nine specific domains are higher than global life satisfaction. For satisfaction with the broader domains (self, possessions, and social life) the means ranged from 4.4 to 5.2, with a mean of 4.8. Again, all broader domain satisfactions are higher than global life satisfaction. It is thought that global judgments of life satisfaction are more susceptible to positivity bias and that domain satisfaction might be more constrained by the concrete realities of an individual’s life (Diener et al. 2000)

Might help to see how this is handled, if at all, with pain scales. For example, I can imagine someone thinking they're having 9/10 or 10/10 pain, say from an injury, but then after something much worse happening, say a cluster headache or a kidney stone, they realize their injury pain was only a 6/10 or 7/10 and the cluster headache or kidney stone was the actual 10/10.

I know there is already some stuff about how the pain scale has cross cultural issues, with people from different cultures reporting and possibly even experience their pain as more or less worse than others from other cultures, so might be an entry point to this line of investigation.