The legislation provides for PPR relief when you have to work abroad (note that the four year limit only applies where you have to move somewhere else within Ireland). I do not think that S 604 (6) sets out to take away the relief granted in S 604 (5) for having to live abroad.
Take a look at this example from the Revenue Guidance notes to the legislation (Part 19 TCA):
On 1 April, 1985, an individual bought a house in Dublin for €50,000. It was her sole residence until 1 January, 1990 when she was required by her employer to work in the USA. Having let her house in Dublin, she worked in the USA until 30 June, 1992. On her return to Dublin on 1 July, 1992 she reoccupied the Dublin house as her sole residence. On 1 April, 1995 she was required to move to Shannon by her employer. Having let the Dublin house again, she moved to Shannon where she stayed in rental accommodation until 31 March, 1999. On her return to Dublin on 1 April, 1999 she once more reoccupied the Dublin home as her sole residence. With effect from 1 April, 2001, she was transferred permanently to Shannon where she bought a new house. Having initially let the Dublin house, she sold it on 1 October, 2002 for €250,000. The chargeable gain on the disposal is computed as follows —
period of ownership 1/4/85 to 30/9/02 17.5 years
period of occupation —
1/4/85 to 31/12/89 (actual) 4 years
1/1/90 to 30/6/92 (deemed) 2 years
1/7/92 to 31/3/95 (actual) 2 years
1/4/95 to 31/3/99 (deemed) 4 years
1/4/99 to 31/3/01 (actual) 2 years
1/10/01 to 30/9/02 (deemed – last year) 1 year
Total 17 years
So - specifically references the property being let whilst working abroad but allows PPR for this period.
BTW, have you paid you NPPR?? Much in the news because of €3k being added on to arrears come Sep 1st