I've started many long sitting diesels with the fuel plus conditioner in almost every case. Other cases had little or no fuel. I never had a failed injector or an engine that wouldn't burn the fuel. On the engines sitting 20 years, I added a proper conditioner, installed a circulation pump drawing from the tank, thru the filters and returned. After the tank was circulated several times, I circulated thru the engine fuel lines. Engines sitting for shorter periods, I add conditioner and let the engine circulate the fuel if it has a high return, otherwise a pump.
My current boat sat for 6 years, no prior mothballing, no issues. There should be a detailed post somewhere. Now I use Archoil 6200. Still running on the same injectors in 2 mains and 2 generators. 1st dose should be 3x normal. Best conditioner I've ever used. Also is a combustion enhancer that will give a 6-10% increase in mileage with new fuel. Available at archoil.com, Amazon or ebay.
If you want details, PM me.