The argument between Abayee and Rav Asi in Bava Mezia pg. 13

It occurred to me on the way back from the sea shore that there is something hard to understand about the argument between Abayee and Rav Asi in Bava Mezia pg. 13..After all, Rav Asi is simply looking for a case where a acquisition is made immediately by the document, so that there will not be a question, "Maybe the document was dated before the acquisition came about?", and thus it would be invalid. So I ask, “What is the difference between that and a document of a loan in which it also would be invalid if written and signed before the loan occurred.” The difference ought not to be that one document is a document of acquisition and the other a document of a loan. The difference ought to be if the acquisition occurred immediately or not. So why does Rav Asi stress the Mishna is talking about a document of acquisition? On another note, I might mention that this might have provided a hint to Reb Chaim of Brisk to make the distinction between a document that causes an acquisition and a document that is only a proof of an acquisition.I think Reb Chaim is coming to answer my question on why Rav Asi goes to a case of a doc of acquisition when a doc of a loan would do just as well. The answer is that to Reb Chaim, a doc that causes acquisition does not need to be dated from the law of the Torah. But a doc of a loan does because it is a doc of proof that needs examination drisha and hakira. That is the point of the gemara in Sandedrin that asks why are doc dated later than the transaction valid? Answer it is a decree of the scribes takana [so that the door will not be shut on those who wish to take out a loan]. So, we see that some doc do need a date from the law of the torah. This seems to bring up a question on Rav Shach that no documents of money are from the Torah except divorce and marriage. But these two kinds do not need a court of law in the first place to make them valid, so there cannot be a law, “ the witnesses in the document are as if their testimony was examined and verified in a court of law.”However, Rav Shach answer that the question of the gemara in Sanhedrin held that monetary documents are from the Torah, but the answer of the gemara is that all monetary documents are derabanan so that the door will not be closed ----------------------------It occurred to me on the way back from the sea shore that there is something hard to understand about the argument between אביי and רב אסי in בבא מציעא דף י''גpg. 13..After all, רב אסי is simply looking for a case where a acquisition is made immediately by the document, so that there will not be a question maybe the document was dated before the acquisition came about, and thus it would be invalid. So I ask, “What is the difference between that and a document of a loan in which it also would be invalid if written and signed before the loan occurred.” The difference ought not to be that one document is a document of acquisition and the other a document of a loan. The difference ought to be if the acquisition occurred immediately or not. So why does רב אסי stress the משנה is talking about a document of acquisition? שטר אקנייתא On another note, I might mention that this might have provided a hint to ר' חיים מבריסקto make the distinction between a document that causes an acquisition and a document that is only a proof of an acquisition.I think רב חיים is coming to answer my question on why רב אסי goes to a case of a שטר of acquisition [שטר אקנייתא] when a doc of a loan would do just as well. The answer is that to רב חיים, a שטר that causes acquisition does not need to be dated by the law of the תורה. But a שטר of a loan does because it is a שטר of proof that needs examination דרישה and חקירה. That is the point of the גמרא in סנהדרין that asks why are doc dated later than the transaction valid? Answer it is a decree of the scribes תקנה [so that the door will not be shut on those who wish to take out a loan]. So, we see that some שטרות do need a date from the law of the תורה. This seems to bring up a question on רב שך that no documents of money are from the Torah except divorce and marriage. But these two kinds do not need a court of law in the first place to make them valid, so there cannot be a law, “ the witnesses in the document are as if their testimony was examined and verified in a court of law.” However, רב שך יכול לענות answer that the question of the גמרא in סנהדרין held that monetary שטרות are from the תורה, but the answer of the גמרא is that all monetary documents are דרבנן so that the door will not be closed