does the din of yitziasso etc. apply to all cases or is it limited to issur niddah. example case of nafka minna if it apllies to kiddushin:
He is Mekadesh someome's daughter with Biya on the eve of her third birthday. the Hachnossa is done before Shkliya [or m'Ess l'Ess] so it does not effect Kiddushin since the Miskadesh is not yet 3 years old. But the Yitziya is done after Shkiya. Would the Yetziya without a Hachnossah effect Kidushin?
Another example: She is almost 12. On her own decision, she aggrees to become Mukudeshes to him via Kedushei Biyah. The Hachnosa is done before she is 12. Her accepting Kedushin is not valid yet so the hachnossah does not effect Kedushin. But the yitziya is done after she is 12. Will the Yetziya alone be enough for kedushei biyah?
This second case has more reason to say the Kedushin takes effect since the Yetziya was accompanied by a Hachnossah (it was done before 12 but after 3) ;; whereas the the Yetziya of the first case did not have any Hachnossah (it was done before 3). Perhaps even by the case of Issur Niddah, the Yetziya is equated to the Hachnossa so that in a case of there being no Hachnossah, even the Yitziya will not be Chayav. (The Mishna uses an expression of equateing the two "Yitziasso [ or Prishasso] Hanoa Lo kBiyasso" "HIS leaveing is as HIS entering" as opposed to saying the Yitziya is an Issur just as the Hachnossa is an Issur. )
An example by Nidda would be the Hacnossa starting just before she was 3 years old; then she has Hargashas Niddah. Would the Yetziya be Assur after Shkiya [or Mease l'Ase] when she turns 3?
By Keddushin there might be more rewson to say that even a Shehiya without any Hacnossah or Yetziya would effect Keddushin even though it will be Pottur regarding Niddah. This might be so since the Kiddushei Biya is effected by Maaseh Ishus, so even a Shehiya might be enough. A Nafka Minnah would be if he or she died before the YeTziya. If Shehiya is enough she would be Mekudeshest to effect the kidushin and the consequent Issurim for the Krovim. She would be an almannah vs a pnuya etc..
See Kidushin 10a -- Techilas Bi'ah Koneh O Sof Bi'ah Koneh. Most Rishonim say that by Kidushin, where the question involves what his Da'as is b'Stam, we say that his Da'as was on Sof Bi'ah. However, if he had explicit Da'as he can be Koneh with Techilas Bi'ah.
However, there may be a Nafka Minah where there is no Techilas Bi'ah such as the case you mention where she was a Ketanah.
P.S I actually believe that if the Ba'al will buy the Kesuvah it will not be Ra'uy.
Please elaborate what you mean to apply from the Sugya in Kedushin.
I would have guessed that the Sof Biyah referred to by the Gmara Kedushin is not the same thing as what the Mishna Shavuyos and Horiyos refers to by "Prishasso". To the contrary, the Shehiya (bNyitzas Tzparnayin etc -or even bMayzid?) is not considered Biya to Mchayav Kareis for Niddah either. so it would seem that whether Shehiya alone could effect Kinyan Kiddushin is still Tzarich Iyun.
If this is correct, there is no proof from that Gmara Kedushin that Prisha (or even the Shehiya which precedes it) would be enough to effect the Kinyan.
As far as your question goes, it still says in the Gemara in Kidushin that "Kol ha'Mekadesh Da'ato Al Gemar Bi'ah," which is surely the Perishah and that without explicit Da'as it is the Sof Bi'ah which makes the Kidushin.
isn't the sof biya the gmar hachnossas haatorah -as opposed to the prisha ?
See Tosfos to Kidushin 10a that this is true only according to the third Teirutz. According to the other three Teirutzim, Tosfos clearly learns that Sof Bi'ah is Sof Bi'ah Mamash.