Oi! Y Niwl! Where are your songs?

I love the fact that all Y Niwl's song titles are numbers - named in the order that they were written, which gives a certain amount of chronology to their releases. It also allows the songs to stand on their own merits rather than by any association with good or bad titles.

But it has made me curious - what has happened to the missing numbers? The world can remain unaware to unreleased/unrecorded songs by most bands. But there's no hiding the fact that Y Niwl have a song, somewhere, called "5" (or "Pump" in Welsh).


So here's the complete/missing songs released so far that I'm aware of. Anyone know the whereabouts of 5, 16 or 20?

1:   Un - first 7" single
2:   Dau - first 7" single
3:   Tri - first 7" single
4:   Pedwar - self-titled album
5: ???
6:   Chwech - self-titled album
7:   Saith - self-titled album
8:   Wyth - self-titled album
10:  Deg - self-titled album
11:  Undegun - self-titled album
12:  Undegdau - self-titled album
13:  Undegtri - self-titled album
14:  Undegpedwar - self-titled album
15:  Undegpump - self-titled album
16: ???
17:  Undegsaith - second 7" single
18:  Undegchwech - second 7" single
19:  Undegnaw - 'Y Niwl 4' 10" EP
20: ???
21:  Dauddegun - 'Y Niwl 4' 10" EP
22:  Dauddegdau - Y Niwl '4' 10" EP
23:  Dauddegtri - 'Y Niwl 4' 10" EP
24:  Dauddegpedwar - 'Y Niwl 4' 10" EP
25:  Dauddegpump - 'Y Niwl 4' 10" EP