Sue, you will find the info in the Medal Rolls free index on Ancestry.
You may need to sign in but you do not need a current subscription. Just go into SEARCH the choose Military then down the right hand side choose Medal Rolls index(free).
Because you are not familiar I should explain how you squeeze all the info fromthe Medal Cards.
Suggest you fill in the search form with George Richardson , in the Regiment section put Labour Corps and in the Number field put his Labour Corps number (I gave you that. It is the number beginning with 4. You will then get a list of answers and the first 2 are the ones you want. As I said there are clearly 2 medal cards for the same person. There is no way that 2 different George Richardsons joined up in 2 different Kings own regiments and both received the same number then both transferred later to the Labour Corps and both were given the same new number. That is asking too much of coincidence.
You can now view and copy both medal cards.
One of the cards shows date of entry into France.
To find when he joined up you need to look at other medal cards for the numbers close to his. Go back to the search form and search for:
Name must be blank
Regiment Kings Own Yorkshire Light Infantry
Regimental Number 12602.
If a named person comes to the top of the list of answers with that number, look at the medal card and see what you get. You now need to repeat for 12603 etc. It is a bit tedious but eventually you will see an answer come up where the person was discharged prematurely. On that card it shows when he signed up. You do the same trick for numbers counting down from 12599 and you will again find a man who was discharged early so you get his date of sign up. Now you know that George was signed up between the two dates. I seem to remember it was between 24th August and 3rd Sept 1914.
Note that some numbers do not come up. That is because sometimes someone signed up but then failed the medical. Their sign up number was then simply lost.
It is a bit tedious, but free
Enjoy
Dave
Ps any problems with that, please let me know