I am looping over different date variables in a graph, that will be my x-axis. The four variables are dates in %tm, %tq, and %th, %ty format. With them, I produce four graphs and then combining them.

I encounter a difficulty when I want to include a vertical xline at a certain date (e.g. 01jan2006) in each graph. When I specify the position of the x-line in %td format it gives me an error in the other cases and if I use values these will be different depending on whether it is measured in months quarters etc. I guess it's just not efficient to loop over type of dates, or is there some clever way to translate the position of the date?

Hope it is clear even without example, I am not sure which example dataset would be suitable to illustrate this.