You two are counting from different points. Deino is saying years between prototype showing up and public appearance. You are saying months between into service and public appearance.
One more thing to add. The appearance can be different as well. The appearance of the first J20 prototype 2001 on the tarmac of CAC, or the appearance of the first operational J-20 in a public air show years later. Both the starting point and ending point can mean differently.
Besides that, there is a chance that H-20 prototype may be spotted some time in 2019 because around August 2018 a very large S-shaped exhaust duct for x-type aircraft was fabricated and handed over to 1st Institute in Xi'an. So the first prototype of H-20 could be in the process of assembly right now. But I don't think XAC is in a hurry to have it taxing on any PLAF or PLA or National day unlike induction of operational piece.