This is probably closer to a comment, but it would be too long.
I suppose that you got the number above 30000 by searching for occurence on the main site. This is an overestimate - I do not know the exact details of how the search engine of Stack Exchange works, but apparently it tries to include words which are close to the one you're searching. You can notice that if you search for occurence among your posts, you get several results which do not actually contain the word occurence. (But they do contain words such as occur, occurs, etc.) This can also be spotted in the search results without additional restriction, if you sort them not by relevance but by some other criterion - such as newest, recently active, etc. - or if you keep the sorting by relevance but look at some of the last pages among the search results.
I would take results from SEDE as a more reliable count, which gives 540 results for occurence. SEDE returns about 3200 results for occurrence. (Still, even if we take these numbers as reliable, the percentage of misspellings is rather high. But we get much smaller percentage and also much smaller number of posts than suggested in the question.) If we check also the comments, SEDE returns 279 comments when searching for occurence.
Another option might be to use search for "occurence" (with the quotation marks), this should search for an exact phrase according to help. This gives only 334 results - I am not sure what is the reason for the difference between this and the results from SEDE. Very likely the results from SEDE include also the posts containing the word "occurences", but this still does not seem as a satisfactory explanation of the difference.
For the words continous, the results from search without and with quotation marks and from SEDE are much closer to each other. (Probably in that case it is much less likely that the search engine finds another word which is close to this.)
Using SEDE we can also find posts which contained some word but it was removed by editing. I found 52 posts for occurence and 967 posts for continous.
Having said that, I certainly appreciate all efforts to improve posts by editing them, be it grammar, spelling, tags, MathJax, or any other aspects. Of course, one should avoid bumping too many old posts at the same time.