If he was attested on 1st May 1811, he wouldn't have been involved in the battle of Albuhera 15 days later. He would have had to undergo medical examination and some basic training in Army drills and musketry before he could be used in battle. The 2nd battalion of the Buffs was the home battalion at that time and would have been used to top up the first battalion, which was deployed in the Peninsula War, when it had casualties.
I think that the earliest that Thomas Prtichard could have joined the 1st Battalion would have been in the autumn of 1811, although the British were not particularly active during the autumn and winter of 1811, and spent their time reconstituting their forces which had been somewhat battered at Albuhera. However if he was back in England/Wales in time to father a child in 1814, it is possible that either he never joined the 1st battalion or that he was invalided out of the Army after only serving for a couple of years or so. He would have originally signed up to serve for 12 years, normally split between 5 years with the Colours (ie active service) and 7 years in the reserve. The Napoleonic wars ended in April 1814 so I don't think it is possible that he could have been with the Ist Battalion at the Battle of Toulouse on 10 April 1814 and back in the UK in time to have a child before the end of the year. While the size of the Army was greatly reduced after the war ended this took some time to happen, with much of Wellington's forces immediately used to occupy France in order to enforce the peace.
And yes it is perfectly possible that the Buffs were recruiting in Shropshire in April/May 1811. There was an enormous push to get new recruits because of the war. I don't know exactly where the Buffs' depot was in 1811, but even if was in Kent, they would have deployed recruiting sergeants around the country to look for likely recruits wherever they could find them. The regiment which might usually have been expected to recruit in the Shropshire area was the 53rd (Shropshire) Regiment of Foot, but their 1st battalion was in India at the time and was not engaged in any hostilities, so less likely to be in need of reinforcements. As a result, the Buffs would not have been seen as poaching by recruiting in Shropshire.
