With respect, or perhaps due to me being unclear, I think you're missing my point.
I am aware that rainbows can spawn at much smaller sizes. My point was, if this was a typical stocker put in at 12" or so, it would still have a couple years to go before it spawned *due to the faster growth of stockers* while they're in a hatchery environment.
A 12" stocker is no more than a couple years old, because it's had a lot of food thrown at it. A 12" mountain-bred wild fish would be very old, 7-8 years, and thus would already have several spawning seasons under its belt.
Stockers don't spawn in their first year in tailwaters either. For all intents and purposes, these are "tailwater" style stockers that have been put in a mountain stream. If they survive, they might hit sexual maturity in a couple years. That 14"er that was shocked up is further along and could possibly spawn this year.
I may not have been very clear in my first post, and if so, I apologize.