If you want to duplicate the hospital test, you need to do so
so that the time intervals are the same.

For example...fast all night, give the glucose tablets (50grams at least) and
monitor the blood for the next 4 hours at least, first thing in the morning with no other food present.

If you do this at night, then the whole night his liver will kick in, and form
new glucose from the amino acids in the protein he ate at dinner.

If his reading of 38 is real and not a lab error, then you need to tag it
in that same time frame. In severe reactive hypoglycemia, the low lows
occur only in a certain time frame. With normal liver action, the blood sugar
then starts to go up again, stabilize. This is called gluconeogenesis. This typically happens when glycogen stores are exhausted.

If you are going to have more tests, for Alan, then just wait until then and
have a new longer GTT done.

I think it is important because very low blood sugars can cause fainting/falling and if not understood, the fall would be unexpected and perhaps dangerously injurious. (for example a neighbor girl had her wisdom teeth taken out one summer in the morning, and fasted, came home, slept, and in the afternoon passed out in shower from low blood sugar--I was outside and heard her sister call for help, so I called 911 for her)

If Alan is undergoing some medical changes in his body, that you have just "caught" early, they could continue to worsen, if you ignore the low reading of 38. So I think you should repeat the tests, with a longer time frame to see if the low low is still there, or was an artifact. If you do not repeat the tests, then trying to see if the low low happens at home is the next best way to check him out. Taking readings while he is eating normal food, may not show anything unless you catch it after a high carb meal.
If he truly has hypoglycemia, he would show some low readings after working out. He would use up his glucose faster than the liver can make new from protein, so it might show up then.

Driving a car, doing a fast paced mental job on your feet with that low blood sugar, is not easy. People do vary in how they respond to low blood sugar.
With Alan's heavy work outs, he may have some stored muscle glycogen that is helping him there. People with less muscle storage would feel weaker faster.

All I am saying is that you need more information. You know many times it is the "common" simple things that sneak up on you to bite you when you least
expect them.