One reason I've noticed for things not showing up on the ICB report is your exact address and Your exact name. For example I had a credit card with Ulster Bank for a few years, did a check with the ICB and it showed up. I since got another credit card with AIB. I did an ICB check and only the AIB card showed up. Afterchecking the original request against the most recent I realised I had given a different address to Ulster bank compared to AIB (I had changed home). Apparently the 2 had not been linked together, and therefore the ICB had no way of knowing that I was the same "Leginos". This may have been unusual in my case as I had a 0.00 balance with Ulster Bank and they weren't issuing statements for zero balances then (This highlighted the fact they had my old address which has since been rectified and I get a statement all the time now).
But I still reckon a personal loan may have worked the same way. For example if I got the loan while i was living with my parents, and then changed address and not informed the bank (statements etc would have gone out to my parent's address and I'd still have collected them), and then took out a new loan with some other provider with my new address, then they would probably not have put the two together. How would they realise that the Leginos living in Clondalkin was the same Leginos who now lived in Dundrum (for example), unless I told one of the banks? Like I said I could easily be wrong but it kinda makes sense.
My brother had the same thing happen when he started using the Irish version of his name a few years back. Also, his home has a house name and a house number which he uses interchangeably. For example,
Leginos Jnr, 1 the Park Rd, Someplace, Some County on ESB Bill
and
Leginos Jnr as Gaeilge, The Brambles, Park Road, Someplace, Some County on NTL Bill.
So when he was opening a bank account his address with the bank depended on which utility bill he gave them!