Is there an easy way to tell a spider which has lost legs apart from a different insect?
Yes. Usually a spider that has lost legs has the full number of legs on the other side. If not then it usually is still retaining a part of it’s leg. To see it look close and maybe with a magnifying glass. Also there may be an uneven gap beetween one leg and another so just closely observe the spider and try to compare it to other spiders that you have seen that look like that one.