formatting dates to automatically extract Year and month

Hello,
I am having trouble with date formatting.
I want to copy and paste large sections of raw data (>5000 lines) and extract the month and year from one of the columns
the date is originally formatted YYYMMDD but sometimes the date appears as DD/MM/YYYY. Some are formatted as a date and others as text.
I've tried applying a custom format (to have everything show as YYYYMMDD) but it only works if I type in each date.
Does anyone know of an automatic way of making everything uniform so that =month() and =year() or left() and mid() equations work?
My goal is to be able to do add data each month and have everything format itself as I paste it in.
Possible?

thanks

Alex

Post a sample file which shows a range of examples of what you have - is the intention to produce proper dates, so that you can use =MONTH and =YEAR in other columns?

Pete