That's a good question which I don't have the answer to. Things used to be less lenient so it would stand to reason that spaces are taken by previous longer sentencees. Ireland doesn't have many spaces to begin with. From wikipedia:
> Prisons and prison population
>There are 12 prisons in the Republic of Ireland with a total bed capacity of 4,106 as of 31 December 2009. The daily average number of prisoners in custody in 2009 was 3,881. However, most of these prisons currently operate at or above capacity.[13] On 25 January 2011 the prison population stood at 4,541. There were about 80 prisoners per 100,000 inhabitants in October 2015,[11] and in Northern Ireland it was 78 per 100,000 in February 2016.
> Prisons and prison population
>There are 12 prisons in the Republic of Ireland with a total bed capacity of 4,106 as of 31 December 2009. The daily average number of prisoners in custody in 2009 was 3,881. However, most of these prisons currently operate at or above capacity.[13] On 25 January 2011 the prison population stood at 4,541. There were about 80 prisoners per 100,000 inhabitants in October 2015,[11] and in Northern Ireland it was 78 per 100,000 in February 2016.