It's quite true that your Perm Res will only need renewing after 5 years.
However, without strictly following your re-entry rules you could end up losing it.
You'll need to present your 13a ACR and be sure that your entry stamp clearly states 13a before moving away from the immigration desk.
If a mistake was made in your entry stamp it can be corrected at the desk, but I'm told despite a mistake it can never be corrected once you've left the desk.
Now, your immigration shows that your AR has been missed for 'n' times.
I have no idea what should be done in that case. Maybe just pay the missing AR fees plus penalties........For that scenario I'd advise further research.
Anyway on the positive side you may well find some delays etc getting a Residence Card issued. But hang on in there and eventually it'll get sorted.