By all accounts, the fourteenth year after Yehoshua led our ancestors across the Jordan into Israel was eventful. That was when the seven and 50 year shemita/yovel cycles began, when many agricultural prohibitions came into effect, and when we all got together at Mt. Gerizim and Mt. Avel to solidly curse out sinners.
Mt. Gerizim and Mt. Avel? Didn’t that happen right away on the very day we crossed the river? Well sure. According to Rabbi Yehuda and Rabbi Eliezer in Yerushalmi Sotah (7:3). Rabbi Yehuda held that the berachos and k’lalos took place at the site we now know as Mt. Gerizim and Mt. Avel. And Rabbi Eliezer held that the Jews made two piles of earth next to the river and called them Mt. Gerizim and Mt. Avel.
However, naturally, I’m referring to Rabbi Yishmael as quoted in that Yerushalmi. As he would have it, the events at Mt. Gerizim and Mt. Avel were only supposed to occur after the seven years of conquest and seven years of division (שבע שכיבשו ושבע שחילקו).
I’ll admit that that was news to me. But the bigger surprise has to be the fact that the two historical events that were supposed to have triggered the transition never actually occurred. At least, not according to Tanach.
May I draw your attention to Yehoshua 18:1.
And all the congregation of the children of Israel gathered at Shilo and they spread there the Tent of Meeting and the land was available for conquest.
As the Radak points out, that obviously happened after the mishkan left Gilgal - which had been its home for the first 14 years. And only then - more than seven years after it was supposed to have completed - could at least one important part of the conquest begin.
And what about the tribal division? Well check out the very next verse:
And there remained among the children of Israel seven tribes who had not divided [i.e., been assigned] their allotments.
In fact, it seems some tribes never received their ancestral land! According to Professor Yoel Elitzur (Places in the Parasha: Biblical Geography and Its Meaning - Parshas Naso), when you compare the lists in Yehoshua 18 with I Divrei Hayamim 6, one could conclude that the tribes of Dan and Shimon never got around to fighting for and claiming their land.
And the conquest itself was manifestly never completed. That is, while it’s obvious from Shoftim 1:27-36 that there were still many Canaanite settlements after the death of Yehoshua, but significant numbers remained even centuries later (I Melachim 9:20).
So where does practical halacha fit in here? After all, the 14 year cut-off seems to be a hard transition point for the status of “trivial” matters like shemita and terumos (Kesuvos 25a).
Rashbam (Berashis 37:2) notwithstanding, It would be plain crazy to suggest that Chazal weren’t aware of Tanach. But I haven’t seen any source that qualifies what looks like an absolute prerequisite for full conquest and full division (see Ritva, for example).
I’m sure that at least some of you will have helpful thoughts on this.
I'm not clear what you are suggesting here? That those tribes never settled in the lands that were allotted to them? That would definitely not be true, we have many verses saying they did (not sure exactly when but eventually). Or just that they didn't expel all the Canaanites right away? That's true, but they didn't expel all the Canaanites from Yehudah either. But eventually the Canaanites went extinct.
See זבחים קיח עמוד ב where the גמ establishes that there were 7 years of division "מדשבע כבשו שבע נמי חלקו" [see חזו"א] I heard from ר שלמה פישר [IIRC I saw it afterwards in בית ישי] that from this גמ it seems that the שבע שכבשו ושבע שחלקו are not statements of historical fact but דינים. Of course they were still being כובש after 7 years, but there was a הלכה that in order to posses א"י they needed to spend 7 years conquering and then 7 years dividing it. The גמ is using a סברא to establish how many years did they have to spend doing חלוקה until א"י would become קדוש.