72 & 24 hour visas

I'm travelling to yangon via Beijing from London:
Ldn Heathrow - Beijing - Yangon
Yangon - Beijing (72 hours) - LDN Heathrow

On the outbound flight, the Beijing to Yangon leg was cancelled by the airline and we were sent via Chengdu with an overnight stopover:

Ldn Heathrow - Beijing - Chengdu (<24 hours) - Yangon
Yangon - Beijing (72 hours) - LDN Heathrow

We used a 24 hour transit in Chengdu on the outbound stopover. Can we use a 72 hour free transit on the return in Beijing?

Thanks