I really value the "Words" feature (effectively, flashcards) available on the web page but unfortunately not the app. I was very disappointed to discover the majority of the words introduced in skill "Past Tense" are missing from "Words". Also, it appears that words are not added to the "Words" list until the Skill is completed, rather than as individual exercises are completed. Eg, it seems I had to finish "Past Tense" for any words in any of the 10 exercises to show up.
Here's what appear to be missing, by exercise (I'm putting apostrophes AFTER vowels to indicate an accent since I'm not familiar with an easy method to enter accents. Eg, o' means an accented o.)
1- fue (1/6) 2- quise, toque', oi' (3/7) 3 - hizo, tuvo, dio, llego', quedaron (5/7) 4 - explico' (1/7) 5 - llevo', recibio', decidio' (3/7) 6 - logro', tomo', miro', abrio' (4/7) 7 - penso', llamo', mostro', entro', siquio', supo' (6/7) 8 - perdio', terminaste, cavo' (3/7) 9 - aparecio', permitio', escribio', conto', obtuvo' (5/6) 10 - alcanzo', saco', nego', considero' (4/6)
An ability to sort/select Words by Skill and by lesson would greatly facilitate study and review (and finding gaps like this).