This is not entirely correct (or at least it's worded a bit weirdly).
If you know that A goes in a certain place you can still try a word using A more than once. It's only once you know that A does not appear twice (because you tried a word containing A twice, and the second A way gray!) then you can no longer use A twice.
In your case you tried MAMMA which contained 2 As and the second one gave you the information that there's no second A.
- FUFFY (8159) (shipping of Faith and Buffy from Buffy the Vampire Slayer)
- IMMIX (4544) (to mix or blend)
- ZOCCO (2142) (low plinth, from the Italian word for sock)
- QAJAQ (530) (alternative form of kayak)
- TRATT (155) (clipping of trattoria)
- KHAPH (7) (alternative form of khaf, the 11th letter of the Hebrew alphabet)
I get the feeling that if this game had 7 steps instead of 6, it would almost always be impossible.
I haven't found a way to win today with 9 steps.
https://gist.github.com/erikcorry/b21723a0ba49c044b03a6030dc...
Edit: Using some of your words you can get to 9 steps (10 including the word you have to avoid): https://gist.github.com/erikcorry/d55d263b129eb7a56c8c212296...
That rule doesn't make sense.
What if the answer is AORTA, and you want to guess ALBUM and then ALPHA?
Why would the last A be yellow and not green? It's the correct letter in the correct location. MAMMA should be gray, yellow, gray, gray, green.