How many prints until you change the top sheet on the printing plate
I’ve only had my X1C for less than a week so can’t speak to number of prints or printing hours until change is needed (for my particular workload). You may have to do a bit of trial and error and just keep bed adhesion in mind as you print more things to determine if it seems to be degrading. It’s important to use the Bambu Lab guidance for cleaning and prepping the various plates for printing.
The following link doesn’t directly answer your question but does offer some initial troubleshooting options if you’re having adhesion problems.