J had ten different TAs in the first 3 years of school - I think he was so challenging that they decided to make him have a couple of shared TAs each year so that they didn't get too tired (or bruised ) as J has full time 1:1 but then they kept leaving...can't think why. Also, every year they tried to swap them round a bit because J gets a bit dependent and attached.
This year, for the first year ever, he's had just one TA all year. It has worked well having all that consistency and also all the training's gone to her, but she's leaving at the end of the year. Had she stayed, he was going to have her, but, tbh, I think he gets too informal when he knows someone well and starts to treat them like he treats me - which isn't conducive to learning! So I'm OK with him getting someone new.
At secondary, TAs tend to change each year, to keep the TAs learning new skills sets and also to stop the children becoming depdendent. I only know of one boy (autistic) who has kept the same TA for 4 years, and that wasn't great because he was then downhill all his final year because he'd got so used to the original TA.
Hope things go well in the end.