Welcome to WebmasterWorld Guest from 184.108.40.206
I changed page titles a month ago, several times...
Several weeks search for "ABC Widget 12345" returned "Results ... of about 164,000 for ABC Widget 12345" response, Google shows up to 1000 of first ranked results, and my page was shown last on last page of SERP!
And now, it is shown in top 50.
1. Why it still was shown, very last in SERPs? There were 164,000 of other results!
2. Why it is now shown in top-50, with old title?
3. What will happen after Google discover that I changed title?
It's always strange and unpredictable...
Why it still was shown, very last in SERPs?
That means your url fell into the -950 style of re-ranking for that keyword - see [webmasterworld.com...] - your preliminary relevance was good, so you are included in the visible results. But then the -950 reranking came into the picture. The frequent title changes apparently tripped this "over-optimization" mechanism.