Carole,
"The fighting ended with the signing of an armistice (cease fire) which went into effect at 11:00 a.m. on November 11, 1918"
1:..... July 29th 1917 Court Martialled Tidworth
2:......August 28th 1917 Dismissed from the service
2:......March 22nd 1918 Base records requests information from London on Ex Capt Harrison's location etc
4:......May 1st 1918 Nora Harrison requesting help and information on her husband
5:......May 3rd 1918 Base records responds to Nora's request for information with no knowledge of AEH's fate or location
6:......June 13th 1917 AIF headquarters Westminister London reports to base records that EX Capt Harrison has applied for Discharge in England
7:......August 28th 1918 Ex Capt Harrison discharged in England
8:......November 11th 1918 War ends
9:......October 10th 1919
(almost a year after War end) Nora receives a message from base Records Australia
(not AIF headquarters Westminister England) undercover of "form of Commission and receipt etc" that Ex Capt Harrison had joined the British Regular Forces as a T2Lt
Because we know nothing of the period between 2: and 7: and again 7: and 9: it's possible that he could have joined at any stage in these two periods. The fact that Nora was informed in Oct 1919 only tells us that the AIF had ascertained his fate and wherebouts on that date. Interestingly he wasn't discharged in England until August 28th 1918 and as I have said previously I don't believe he could rejoin a service until he was Discharged.....? But nothing confirmed here?

?
If he joined after August 28th he would be joining the service (the War) for a couple of months, but he joined the Regular Forces, I think he would have to join for several years war or no war?
Whatever!!! he joined the regular forces quite late in the War and quite possibly his records aren't with the rest in the normal manner particularly if he was in the service after 1920
Ian