This certainly raises a question about the amount of gratuity his widow
received.
Gratuity was calculated from enlistment providing the man served overseas at some point
which obviously he did.
There were disqualifying periods as listed below courtesy of the LLT:
Service previous to date of conviction for desertion, unless that service had been restored under King’s Regulations;
Any period of penal servitude, imprisonment or detention exceeding 28 days;
Any continuous period of absence without leave exceeding 28 days;
Any period of service in which the man had been in receipt of civilian wages (for example, as a member of Class W Army Reserve).
From this it's quite possibly he went into Reserve ( & back to his day job) as his Btn.
were still UK based & recalled just prior to embarkation.
This was quite a common occurrence.
Academic really as AllanUK has given the probable attestation date.
As an aside he was at Berneville France W. of Arras on the day he died.
This was at the beginning of the German Spring Offensive.