I understand you line of thinking but maybe need to clarify my point a little.
If you look at it from a lawyer end of it you are assuming that the FBI said there was no heart shaped adhesive residue. It only states "sticker or sticker fragments". If there was no adhesive residue, they would have said "no stickers or sticker fragments or adhesive residue". They are very specific in the way they report it. If they didn't say it, you cannot assume it. Apparently the adhesive residue was visible to the naked eye. They might not have even asked the FBI to look for it. Or if they did test it and compare it to the sticker found, it may be in a separate report that we haven't seen yet.
JMHO.
There's no way I believe that if there was heart-shaped residue on tape that the FBI examined they would not mention it, whether seen by the naked eye or microscopically.
I will definitely believe this if someone can give me the page number of the FBI report (not LE's own synopsis) that confirms this finding because I deal in facts, otherwise its hearsay, not that I would be surprised if a heart sticker was on the tape because that could indicate several things.