Tom Riker was just as responsible for what happened on Nervala IV as Will Riker was. If Will received a commendation and a promotion for his actions there, Tom should have, too.
This.
The acts of valor that Will was promoted for occurred before the second pattern was created and reflected.
OK I misunderstood. Yes, I agree, any act of valor conducted during the mission on that planet prior to the transport split should be applied equally to both Will and Tom.
Tom Riker should have got the same commendation, but not sure about promotion (commendation does not = promotion, they are 2 separate things). Yes, if he was fit for duty, he "deserved" to be promoted from Lieutenant to Lieutenant Commander, and probably did actually receive the same commendation (we don't know, just have to speculate),as well as another commendation for living on Nervala 4 alone for 8 years! But that doesn't mean Riker gets an automatic promotion and gets to bump the current first officer of the USS Hood.
In Second Chances he gets a new post on the Ghandi. They never said if Tom Riker was promoted or not, but how would the military handle some soldier or sailor found alone on a deserted island for 8 years. They would make sure he didn't go crazy and was fit for duty. So with Tom Riker, Starfleet was probably waiting the mental evaluation and on paper work or something, before promoting Tom Riker. Tom Riker himself even said he needed to be acclimated after living alone for 8 years.
But as we know, Tom Riker wasn't mentally fit for duty, and he quickly got bored, joined the Maquis, and stole the Defiant. So whatever rank he may have or may not have had, doesn't matter because Starfleet would have stripped him of his rank (probably busted him to crewman), drummed him out with a dishonorable discharge, and imprisoned him anyway, if the Cardassians hadn't captured him first.
Any act of valor on Will Riker's part after the split, is Will Riker's alone, though. Likewise, Tom Riker would have owned both any valorous acts (8 years alone on Nervala 4 qualifies!) after the split, and
also owns his disobeying orders, joining the Maquis, and theft of the Defiant.