Is there mature sperm cells from the epidymis everytime we ejaculate?

Yes! All sperm passes from the testes through the epididymis where they mature, on its way through the vas deferens. Mature sperm is ejaculated. https://pubmed.ncbi.nlm.nih.gov/12672117/#:~:text=Mammalian%20spermatozoa%20undergo%20morphological%2C%20biochemical,the%20epididymis%20(epididymal%20maturation).

They are made in the testicle- pass thru the epidi. and vas- stored in the seminal vesicle and discharged with ejaculation