Software Metrics: function points and lines of code

I have read a lot of papers and books that try to relate funtion points and lines of code.
The final step is always a big table with the lines of code for function point in every language.

Then the thesys is that is possible to derive the "effort" in man/month, given the fp count and the derived program dimension.

I think that there is a big mistake. In my experience to deliver 1M of lines of code I have to develop 1.5M of lines, and as my program get older, I still deliver 1M of LOCS, continuing to produce new lines that replace the old one.

A stronger example: as I develop new lines to correct errors, the User Manual (and the user interface) is always the same!

The real effort is related to LoC that I write, that are more then LoC that I deliver.