Let's check the spell descriptions and find out why not.
You touch a creature that has been dead for no longer than 200 years and that died for any reason except old age. If the creature's soul is free and willing, it's restored to life with all its hit points.
Since the polymorphed creature is not dead, it cannot be resurrected using true resurrection.
Touch a creature that's died in the last minute. It returns to life with 1 hit point. This spell can't return life to a creature that died of old age, and it can't restore missing body parts.
Since our polymorphed creature has not died in the last minute, they cannot be revivified.
Touch a creature dead for no longer than 10 days. If its soul is both willing and at liberty to rejoin the body, the creature returns to life with 1 hit point. This spell has no effect on undead.
Since the polymorphed creature is not dead, they cannot be brought back using Raise Dead.
Since spells only do what they say they do, I do not think true polymporph can be combined with any of the above spells.