IMAP ios sync help!

I have recently started to use my icloud IMAP email address in addition to the email address that I have had for years.

I am starting to copy emails from numerous folders contained within a Outlook PST file to newly created IMAP folders in my new email account BUT not all of the emails that are being copied are showing on my iPhone & iPad.

For example - One folder I moved across had 500 emails contained within it - I dragged all of these emails from the original PST folder to a newly created IMAP account folder. Within Outlook, all 500 of the emails are now visible within the new IMAP folder. On each ios device, only about 200 of the emails are showing in the newly created folder (the same 200 on each Ios device) - Where are the other 300 emails being stored and why are they visible in the IMAp folder in Outlook but not in the IMAP folder on my other devices?

Outlook 2013 in use on a Windows 8.1 PC

ios 8.4 in use on both iPhone & iPad.

Many thanks in advance,

Mike.