So I was exporting a sequence last night not realizing the space on my hard drive was getting low so it ended the export at photo 611. I made some more space and went to restart the export and have the initial sequence number start at 612 (selected just 3 photos to test, 612, 613, 614)
Instead of then putting those numbers as 612, 613, ect, it overwrote 1, 2, and 3 at the beginning of the sequence..

This happened to me before on LRT4 I ended up just deleting the whole sequence and restarting, would like to avoid having to reexport everything though.

Please do another test with a short test sequence (10 images should be enough, export 5 and then the next five with "initial sequence number" = 6. Let me know. In all my tests this works.