Just because you take early retirement does not mean you cannot be looking for other sort of work, people take early retirement all the time and start working again straight away. For example gardai, who can retire quite early. If you are looking for work then you can sign on for jobseekers benefit, retired or not, am almost, (note almost!) positive of this.
In my own situation my benefit has run out, I am still seeking work and do not qualify for jobseekers allowance so I sign once a month for credits to maintain my prsi record for pension. Some former colleagues of mine actually got early retirement and have a pension payment and they were able to draw their jb because they were looking for another job. AFAIK the entitlement to full pension is worked out by some calculation of average payments per year based on the number of years from when you started work to normal retirement age, I would be afraid that the government would change the goalposts on this in the future so intend to continue signing for credits even though at the moment I would probably have enough actual paid contributions.