depends on what brand you use. some acrylic. i have got the acrylic with the blue plastic protective tape. that comes off easy. the paper will tear often if its cold. its not an old tank issue specifically. half the walk through videos of working with acrylic talk about how hard the paper can be to remove.
The problem with paper on old/used tank bottoms is its usually already torn in places from being moved and also been wet before. After being wet it dries hard and is unable to be peeled off at all. Even if u can manage to get the paper part way off the glue is left behind. It really is a nightmare to deal with lol… paint scraper, razor blade or sanding is the only way. New paper is a breeze i agree.