Recently I've found myself willing to answer a question from users who previously posted a significant number of questions before, using info from their previous questions that I think are relevant to answer their latest question. I am bothered by the fact that they didn't include that info again in their latest post (did they forget, did they think it was not relevant?) and found myself reluctant to the idea of mentioning said info in my answer, as I don't want to recall facts they possibly didn't want to mention in their newest post.
On the pro-side (ie "yes, we may use info from previous posts"), there are several things to be considered:
Everything one posts on the Stack Exchange network is publicly available and "stays forever", so using that info does not break the site's rules (and I would not tell anything that was said by OP on SE already),
Said info may help in writing a better answer to OP's issues.
On the con-side:
It feels like breaking OP's trust, should they didn't want this info to be disclosed/considered in this particular question (not everyone scrapes the site to get to know as much as they can from someone and maybe OP would expect this info to be mentioned only in one specific question),
Mentioning info from another question may make other users' experience harder ("how do they know that? I can't find it anywhere in OP's question!")
Regarding the abovementioned I still can't make my mind on whether it is okay to do so. Asking OP in question's comments if they're okay that I use info XYZ from question ABC doesn't feel either because this links to the info already.
Should we include publicly available info from a user's previous posts when we think it may help in writing a better answer to their latest question?