Not sure where your figures are from. 7,249 according to this article which raises more sinister issues:
0ver 60% of EU citizens stopped at border are Romanian
There was plenty of opportunity to apply for settled, or pre-settled status but bound to be some people who didn't bother or couldn't produce all the evidence required.
Seasonal workers more likely to have problems securing it though. You have to produce a lot of paperwork to prove you've been living in the U.K.
My FiL didn't even have a valid passport to prove who he is! You would think it would be easy for someone granted ILR in the early 60's, 4 years after arriving in the UK but you can see how the Windrush scandal came about.
There simply isn't a perfect way to do it. We have no idea who is in the country and whether they are here legally.