Hi Mike,
I've had a quick look for any service records for Henry (Harry) Frost but with no luck but if you could post any personnel details on Harry eg. Date and place of birth this would help narrow the search. It's also possible Harrys' records may have been destroyed during the Blitz (60% of the records were destroyed).
I can give you a little more information from Henry's Medal Index Card:
Henry was entitled to the 1915 Star, British & Victory medals. Interestingly the SWB List F/A/119 entry at the bottom means Henry received wounds/illness during his service and was awarded the Silver War Badge. He was discharged on the 21/2/18 which suggests to me that his discharge was due to the wounds or illness received from active service.
The only way you can 100% confirm which Battalion he served in would be to check the Medal Index Rolls for the South Staffordshire Regiment and this lists the soldiers Battalion he served in to gain his medal entitlements. The Silver War Badge entry will give information on the date of enlistment, discharge and if the Badge was issued due to wounds or illness. The problem is these rolls are not available to view online and are held at the Nation Archive in Kew
We know Harry first saw service in the Balkans with the South Staffs on the 6th October 1915 and the code 2B refers to Gallipoli. I've taken a look at the the movements of the South Staffs Battalions during the war and I think Harry may have served with the 7th (Service) Battalion. The 7th Battalion went to Gallipoli in July 1915 and It's quite possible that Harry was sent later with others to join the Battalion to replace casualties etc.
7th (Service) Battalion
Formed at Lichfield in August 1914 as part of K1 and became part of 33rd Brigade in 11th (Northern) Division. Moved initially to Grantham. Moved to Frensham in April 1915.
Sailed from Liverpool in early July 1915 for Gallipoli, landing at Suvla Bay 7 August 1915.
Evacuated from Gallipoli December 1915, moved to Egypt via Imbros.
Moved to France in July 1916.
The best information we could find would be from his service records which would confirm lots and lots of information.
I hope this helps a little.
Kind regards
Adrian