Wow what can I say...

Completely bypassed my multitude of steps in one quick go.
Thank you, thank you, thank you

The reason for the padding is that the folders are stored within a records management system. The PN and the five numbers or nine numbers with padding ensures they are all sorted in numeric order when viewed in Explorer.
Plan numbers between 1 and 99999 will always have five digit padding.
Plan numbers between 100000 and 999999999 will always have nine digit padding.

I can easily work with what you have done regarding the nine digit numbers.

Thank you again Andrew, very much appreciated.

Regards, David