It would be nice if athletic directors at schools knew this stuff, but they haven’t, in my kids’ experience; Ivy coaches and kids who have been through the process of Ivy recruiting are the best source for answers.
Sooo…in my experience ( 2 rowers, Ivy recruiting), once you’ve been to your OV, and the coaches (hopefully!) offer you a slot, they will tell you that you will (assuming all goes well, and it usually does) receive a likely letter within X days after your complete ED application has been submitted.
Between them, my kids have gone over the recruiting process with rowing coaches from 6 or 7 Ivies at this point, and likely letters have consistently been discussed as an end result. I’d be much less comfortable than fenwaypark is in believing I really had a slot if a likely wasn’t mentioned; in fact, I worry that this is one of those cases where an athlete might believe more support is being offered than is actually the case, as Ivy coaches do offer softer support as well. I can imagine cases where a likely might not be offered, but as exceptions that prove the rule (for example, when an athlete commits close to the ED decision date, the admissions committee might not bother with a likely).
That said, experienced coaches don’t usually offer OVs to athletes unless they think they’ll pass the pre-read process. It sounds like you’re in a good position, but don’t be afraid to ask the coaches where you stand in terms of their available slots. As fenway stated, you’ll want both a positive pre-read from admissions and a positive offer of a slot from the coaches before you commit to an EA application–and again, I’d want to hear the words “likely letter” to be convinced that I really had both of those things.