If you have given the accountant all the year end stuff, personally I wouldn't post anything else dated June. Your best bet, though, is to have a word with the accountant, s/he may not have done any work on the backup you sent yet (they don't always start straight away) and if this is the case you could enter them with the correct dates and send a further backup.
I would not enter them onto sage. I would do the Sage year end and enter the invoices as the 1st of the month in the new year.
Speak to the accountant and arrange for copies to be sent over to them. The accountant will treat these as afterdate Invoices and make the relevant adjustments in the year end accounts to account for them.
Then once the accounts are done, the accountant should provide you with some year end adjustments to post onto sage as of the 1st of the month in the new year so that those additional expenses do not get counted in the new year.
