Privately owned tombs were meant to cover familial and public emotions – they were designed to prevent the presence of unwanted strangers and any "leak" of the corpse's defilement out of the tomb.
Since the Sanhedrin owned its tombs, it could "lend" a burial place "on demand" when the Sanhedrin executed a Jewish felon. We've already seen that by law, felons' bodies had to "dwell" in the Sanhedrin tomb for a year.
- It assumes that the all of the laws that were in vogue in 30 CE were still known and active in 190 CE. It is quite possible that there were other practices that were dropped or introduced during the interval.
- It assumes that the Mishnah is descriptive rather than prescriptive. What I mean is, it assumes that because something was legislated that it actually happened. We could point to many instances in which things happen that are contrary to the law. Just because something is prescribed does not mean that it always (if ever) happened that way.
- It assumes that we have enough information in the Gospels that we can use the Mishnah to interpret them so easily. But the Gospels do not promote a "temporary burial". Their focus is on the claim of resurrection. Thus while there are certainly some historical facts that might tease us, the authors were not trying to provide us a legal description of Jesus' burial. The purpose was to move the story on to its climax. Thus, a lot of important details are not present and makes a full legal analysis impossible.