The old armour for sale is normal; you can also buy back the eye of the cyclops from the warrior's guild master after his first test. If you did not hit alt or move the fixed armour in your inventory after talking to Grischa but before saving, you should have been able to re-load and get different stats, though.
The dragon heart is required for the second warrior's guild test, so if you did this quest first the other would be broken if you could not buy it back. Also, as you found, the 'fixed' armour is not necessarily better. Ideally, the head of the warrior's guild would recognize that you have the heart forged into the armour, and the heart would add an effect/stats to the armour, rather than getting a completely new set.
