Thank you for your further searching. Letitia and her husband Charles Lynn were in and out of the workhouse with their children, sometimes just the children. They ended up on their own at a home in Swansea for a while. Herbert later changed his name to Victor. I have his service records that give information on his military life but other than the tracer card, nothing else for David George Lynn. He was called just George in one entry at the workhouse. I have information on their sister, Lily Lynn and her family but David just seems to disappear.
As the tracer card is in the name of David G Lynn, I can only assume that he went by the name David, if this is indeed the David G Lynn that I am looking for. It is odd that only his tracer card can be found to date, no other military or civilian records. Royal Artillery information or 1911 or 1939 census information may help in finding him but these are only available via subscription.