I assume he is the Frank George Bibbs from Pontardawe/Birmingham areas. (as per a Public Tree on Ancestry etc)
The conditions for issue of the Territorial as decribed by Jim can be seen here (scroll down)
http://www.1914-1918.net/soldiers/themedals.htmlI would say it is highly liklely he was with one of the 'Welsh Field Ambulance' units of the Territorial Force prior to transferring to 'Regular' RAMC.
He was certainly with the Colours in November 1914 as this Roll of Honour shows ( under Tareni Colliery, Godre'r Graig)
http://welshnewspapers.llgc.org.uk/en/page/view/4097923/ART87He was home sick from France end of 1916 during which time he was presented with a wrist watch by the Church.
http://welshnewspapers.llgc.org.uk/en/page/view/3978711/ART69/frank%20bibbsHe was wounded by shrapnel to the nose in May 1918
http://welshnewspapers.llgc.org.uk/en/page/view/4115886/ART102/frank%20bibbsI would say that the 88918 number is too high for a 1914 man and that he transferred to 'Regular' RAMC at some stage from his Territorial (TF) unit. This would be before he went overseas otherwise the TF number would be on his medal card. He would have had a number prior to the 88918 number.
If you want to pinpoint the transfer date then look for papers on numbers around it.
E g. In Pensions put 889* in Regimental Number and med* in Regiment and you will get about 6 RAMC men whose numbers start with 889 (ignore those not a 5 digit number) Repeat with 888* , 890* etc. Bear in mind that his service will not necessarily mirror that of numbers near his in terms of units served.All this excersise does is give an idea of when that number 88918 was allocated.
The Colliery reference might be worth exploring. All told what with the TF RAMC link etc there's a good chance he was in their first aid/rescue teams. Might be worth seeing if the Colliery papers have survived in one of the Glamorgan Archives.
Gwil