Thanks - I've just found the version number issue hidden in the Usage manual!
But the double newline issue is still an annoyance - it seriously reduces the amount of text I can get on a screen. I've looked at the files with a hex editor and it's interesting. I'm using Frescobaldi to generate the files, and it seems that this uses only hex 0A as a line delimiter (very Unix). Convert-ly replaces this with hex 0A 0A. But it's not consistent, and I don't recall this happening in previous conversions. The snippets below show the differences. I'd like to report this as a bug, but the link to gmane on the LP website is broken.
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Sunday, December 18, 2016, 2:45:37 PM, you wrote:
> 2016-12-18 15:08 GMT+01:00 Peter Toye <address@hidden>:
>> Thomas,
>> Thanks. It just looks odd that the convert.ly issued with .52 only updates
>> to .49
> This is a misunderstanding.
> convert-ly from lilypond-2.19.52 _does_ update to 2.19.52.
> Or more precisely: all syntax-changes for which a convert-rule exist
> are applied up to 2.19.52.
> It does not change the version-statement of your file to the
> lilypond-version of convert-ly you actually use, but to the version of
> the latest convert-rule.
> In general, convert-ly converts syntax of ly-files to be compilable
> with the LilyPond-version matching the version of convert-ly.
> There is no need to change the version-statement to make it compile
> with 2.19.52 at all. You could even compile a very old 2.12.3-file
> with 2.19.52 (granted the syntax of the old file will work).
> The reason to change the version-statement to the version of the
> latest convert-rule is more to issue an error, if a converted file is
> compiled with an older ly-version, like:
> error: program too old: 2.16.2 (file requires: 2.19.52)