Board a train in Pingyao with a ticket from Linfen

Hello! I want to take a D-type from Pingyao to Beijing. Sadly all were sold (within minutes). Now I saw that there are some available from Linfen to Beijing on the same ride. Linfen is the city where the trip starts. Is it possible to buy Linfen-Beijing trip but board in Pingyao instead of Linfen? So would I have problems in boarding and get the seat who is reserved since Linfen? Happy to get answers from you to clear this up!