pawras Hi mate ,yep a good point , obviously in the scale of the sample , the number in that situation i'm sure is very small against the population ,but the way i set it up in HRB catches only the move to the new yard , then 1st run , then 2nd , 3rd and so on. If the horse moves to another yard he would show up there in the new trainers stats as well, starting with the move , then 1st run , 2nd run etc. It would be 2 different situations - 2 sets of stats . But then a return to the first trainer i don't think i would catch that in HRB , due to it's limitations as in the database the horse would have previous runs for that trainer and could possibly corrupt the data slightly eg- if he had 5 runs the first time then left, he would be showing up again when back as a sixth run , where as technically it should still be classed as a "new" move. To catch these i would have to check every individual run and that would be impossible.
Once a pattern is established (see attached eg A Balding) , i usually drill down deeper with that trainer and look at other factors , a certain type , age , racetype and from doing that i have to say that a return back to a previous trainer does happen but is quite rare in the scale of things.
In this case i would be looking extremely closely at Baldings "new recruits" on their 3rd start till 5th - i would like to see some recency with this pattern , then i would profile his runners within that range - hcaps , age , sex , career runs etc etc.
There are trainers who have clear patterns - Cumani is very good on the first run (34%) , although did not have any new recruits last season , so is Johnstone & Varian but once again had few runners last season. Tim Vaughan was brilliant first time with new recruits (25%) up to 2012 but since then has been dreadful , so you do have to dig a bit deeper - others like to run them to fitness , and it usually coincides with a drop in ratings ,then 5th or 6th run their ready to compete. I do the same with horses coming off layoffs and with headgear and having the stats just provides some extra insight when looking at the form.