I forget no such thing.
...they probably regarded the burial linens with His blood all over them as sacred from the very first moments.
Practically the first thing that Joseph and Nicodemus did with the body after getting it from the Romans would have been to wash it completely. I don't suppose that the body had been completely exsanguinated, but the fact that "blood and water" issued from the spear wound (inflicted after death) showed that the blood had already started to coagulate and settle. There would be no blood on the graveclothes.
Between Calvary and Ascension Day, the disciples saw Jesus repeatedly. I doubt very much that they bothered at all with either the tomb or anything in it, after they had seen the Lord Himself alive again. Mary Magdalene grabbed Him by the ankles on their first meeting after the Resurrection, as if never to let Him go. She, of all people, would be the last to concern herself with a bundle of discarded textile products — at least, until it was too late for going back to look for them. Especially ones that had been on a dead body, which would make them ritually unclean.
As to what the disciples understood about the meaning of Christ's blood, they heard him talk about it, but it was over 50 years before John wrote most of it down. It took years for the disciples to understand it. At the time, they understood practically nothing, as we can see from the Synoptic Gospels. They were completely blindsided by the Crucifixion, despite repeated assertions by Jesus that He was going to Jerusalem to suffer and die. The Resurrection caught them no less "on the hop", again despite repeated statements from the Master. Ironically, it was the authorities who took more note of those predictions than the disciples did, since it was they who posted a security detail on the tomb.
The Apostles understood all about Christ’s body and blood as soon as they experienced the Pentecost, not years later.
Everything about Christ was against the common thinking of the day; the women loved Him and would have gathered the garments with any trace of His touch. Remember that people were healed simply by touching the hem of His garment in their presence; it makes perfect sense that they would treasure any article Christ had contact with.
They had to hurriedly inter Christ because of the Sabbath, so they didn’t get to prepare His body the way it was usually done. That’s why they went back later: to finish the job properly. They saw something miraculous had happened; wouldn’t it be logical to gather up the evidence of something miraculous to them? I think so.