It takes three decades to "build-up" data sets. Historical temperature measurements from around the globe have been kept since the 1800s.
What you mean is that it takes three decades for climate alarmists to re-adjust the old raw temperature records to support their assertions. Which is exactly what is wrong with "climate science".
I can only guess most, if not all, scientists/scholars/researchers should have their professional training, skills, ethics, protocol and system to produce their conclusions/suggestions that could be right or wrong years later.
Basically, I think the scientists can only do and say right now is what exactly they currently believe is right for now, according to conventionally scientific research methodologies/protocols.
Of course, there is possibility for re-adjusting old raw records by certain researchers as you guess, but I think the probability should be extremely slim.
Besides, adjusting raw data records, such as outliers, might be a proper and normal step in standard research protocol, if the adjustments are based on strong scientific reasons/causes. I just guess.
We usually very much believe scientists, and their update of scientific knowledge from time to time. Why not this time?
If someone truly believes the raw data has been compromised/changed, however no solid proof could be found Yet about the adjustment, then the argument hence created will be a never ending one, that could spend unlimited time for almost zero result - nearly guaranteed.
Personally I don't understand well the objective of climate scepticism. Is it simply for social justice, proving the alarmists lied for their wrongdoing of adjusting data?
Good luck to the evangelists of climate scepticism! They do have unusually great courage!
Perhaps they deadly need a whistle-blower! Perhaps a potential whistle-blower would show up anytime soon! We never know!