If a card says "Can only be special summon by the effect of ____" does that mean you can't Reborn it or use any other kind of card to bring it back from the graveyard?

if the card says this card can only be ss by blah blah effect then it can be brought back with coth or reborn

however if it says cant be ss EXCEPT by blah blah effect then it cant be brought back i think

there is another thread about this called Special Summoning from grave yard
answers a lot about this

That's almost correct.

If a monster says "This card can only be Special Summoned by..." then you can revive it with COTH or Premature ONLY if the monster was summoned properly first and it went straight from the field to the grave. This also applies for all Ritual monsters and most Fusion monsters.