I could take 1 unit today and it will drop me a different amount to what it will do tomorrow. If I take 1 unit just after I've eaten or when I'm ill, or when I'm stressed it might have absolutely no effect or I could rise in spite of it. It depends on what else is going on in my body at the time.
If you're drinking 3 litres of beer a day and not eating proper meals you're probably under nourished and, frankly, alcoholic. That's going to have an impact on your insulin sensitivity factor. Our background insulin essentially works to deal with the trickle of glucose let out from our liver when we aren't eating. Your liver can only do one thing at a time so if it's busy processing alcohol, it won't be trickling out glucose. You might want to seek a liver funtionction test to check the impact of all that alcohol on your liver.
So if correction doses aren't having the effect you expect, you might need to recalculate your insulin sensitivity factor and maybe your I:c ratio. But neither formula is a fixed, set in stone thing. You might work out that one unit drops you 4, but it won't drop you 4 if you take it when you have just been for a rum and all the exercise has made you really insulin sensitive, or if you take it just before you get in a hot shower, or befor a really stressful meeting with your boss. Sometimes we are just more or less sensitive to insulin depending on what's going on, it's wise to change doses to take that into account and sometimes we just have to expect the unexpected. So blood sugars are inherently unpredictable.
If you really think it's a problem with your insulin, chuck it out and start a new pen/vial.