Form 8582 for passive activity losses was not generated and filed last year, only schedule E. How can I know if the loss on schedule E was deducted already?

By looking at Schedule 1 of your last year's tax return on line 5.  If the amount there is the same amount that is on your Schedule E then all of the loss was deducted.

Since you do not have a Form 8582 the loss was probably all deducted.

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