Tested this in game with items using the new smithing progress. When hitting for the last time, the message appears stating your item is done, but no xp drop occurs for the last remaining xp. This results in slightly less xp earned than the item is worth.
For instance, a rune dagger is worth 480 xp and awards 8 xp per hit under normal conditions at best heat. The last hit, worth 8 xp, isn't awarded, resulting in a loss of 1.67% of the total xp.
I’ve passed this post on for you :)