Dude, GUS is the last place you want to go for information on demographics, residency etc.
They have hard data, which for some things is very reliable.
idiots said in 2020 that the population of Gdańsk is 486542
Actually they didn't, as the GUS Demographic Yearbook 2020 makes clear.
social services estimate that
You do know what the word "estimate" means, don't you? Here's an example of how to use it in a sentence: GUS do not estimate that the number of Brits who have a valid residency permit of any type in Poland is 7,510, GUS know that the number is 7,510 and they can tell you where and when those permits were issued and to whom.
Also, those "social services", do they get more money or less money based on supposedly needing to provide services to more people? So, they have an vested interest in what the number of Ukrainians in Gdansk is taken to be. GUS, on the other hand, don't care whether the number of Brits who have residency permits in Poland is seven, seventy or seven hundred thousand.
The system of population evidence in Poland is archaic and wildly inaccurate
It's actually very up-to-date and accurate for Brits: if we don't have our papers in order. we'll be pulled over when trying to leave the Schengen Zone or refused entry to the Schengen Zone. Which is why one can say with a huge degee of confidence that Brits are not a source of demand for tens of thousands of flats/houses in Poland.