tense - "Didn't use to get" or "Didn't used to get"?

I just made a minor grammar correction on Travel SE, and another user said the grammar correction was unnecessary.

The original text was

Another factor--sometimes life happens and you can't fly. In the old days you could simply sell your ticket to someone else, now you either have to eat a hefty change fee or lose it outright. That's money in their pockets that they didn't used to get.

It was corrected to:

Another factor--sometimes life happens and you can't fly. In the old days you could simply sell your ticket to someone else, now you either have to eat a hefty change fee or lose it outright. That's money in their pockets that they didn't use to get.

1. Was this grammatical correction an improvement?


2. Was the original text grammatically correct?



3. Is the edited text grammatically correct?

Answer

Both are acceptable (yes, I know I'm the one who said you were wrong), but used will induce fewer corrections :)

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Various opinions:

English Grammar Today has this to say on this exact topic:

The negative of used to is most commonly didn’t use(d) to. Sometimes we write it with a final -d, sometimes not. Both forms are common, but many people consider the form with the final -d to be incorrect, and you should not use it in exams:

It didn’t use to be so crowded in the shops as it is nowadays.

I didn’t used to like broccoli when I was younger, but I love it now. (Don’t use this form in exams.)

In very formal styles, we can use the negative form used not to:

She used not to live as poorly as she does now.

Language Log suggests that used is preferred by English users at large (but of course as good descriptivists they offer no comment on which should be preferred...)

Over at EL&U use is agreed to be 'more correct', but is firmly in second place behind 'rewrite to avoid'.

BBC World Service Learning English is firmly use.