ggplot, drawing lines across multiple facets (x axis is date) - ggplot2

Question

My question is almost identical to this question EXCEPT that I am using dates for my x axis. I have tried the code from the answer in the linked question. The example provided works for me, but I cannot get it to work for my dataset. I am guessing it is because of the dates?
(Sorry I could not comment on the previous question chain - I'm new and don't have enough points to comment)
Here is the sample code:
library(ggplot2)
library(gtable)
library(grid)
data<-data.frame(Date=rep(seq(as.Date("2018-09-22","%Y-%m-%d"),
as.Date("2019-06-19","%Y-%m-%d"),
by=30),9),
Station=c(rep("A",30),rep("B",30),rep("C",30)),
Description=rep(c(rep("Var1",10),rep("Var2",10),
rep("Var3",10)),3),
Data=c(seq(1,10,by=1),seq(500,800,length.out=10),seq(30,90,length.out=10), seq(5,19,length.out=10),seq(450,1080,length.out=10),seq(20,60,length.out=10), seq(2,15,length.out=10),seq(600,750,length.out=10),seq(80,25,length.out=10)))
plot<-ggplot(data,aes(x=Date,y=Data,color=as.factor(Station)))+
geom_line(size=1)+
facet_grid(Description~.,scales="free_y",switch="y")+
xlab("")+
ylab("")+
theme(panel.background=element_blank(),
panel.grid.major.y=element_line(color="grey80",
size=0.25),
panel.grid.major.x=element_blank(),
axis.line=element_line(color="black"),
strip.placement="outside",
strip.background=element_blank(),
legend.position="top",
legend.key=element_blank(),
legend.title=element_blank())
plot
plot.b<-ggplot_build(plot)
plot.g<-ggplot_gtable(plot.b)
data2npc <- function(x, panel = 1L, axis = "x") {
range <- plot.b$layout$panel_params[[panel]][[paste0(axis,".range")]]
scales::rescale(c(range, x), c(0,1))[-c(1,2)]
}
start <- sapply(as.Date("2018-10-10"),"%Y-%m-%d"), data2npc, panel=1, axis="x")
plot.g <- gtable_add_grob(plot.g, segmentsGrob(x0=start, x1=start, y0=0, y1=1, gp=gpar(lty=2)), t=7, b=9,l=5)
grid.newpage()
grid.draw(plot.g)
resulting plot

Answer 1

I have figured out my own answer!
The key is in changing t, b, and l in gtable_add_grob:
plot.g <- gtable_add_grob(plot.g, segmentsGrob(x0=start, x1=start, y0=0, y1=1, gp=gpar(lty=2)), t=7, b=13,l=7)
Although, it seems to me to be trial and error to identify the correct values of t,b, and l.
New code:
library(ggplot2)
library(gtable)
library(grid)
data<-data.frame(Date=rep(seq(as.Date("2018-09-22","%Y-%m-%d"),
as.Date("2019-06-19","%Y-%m-%d"),
by=30),9),
Station=c(rep("A",30),rep("B",30),rep("C",30)),
Description=rep(c(rep("Var1",10),rep("Var2",10),
rep("Var3",10)),3),
Data=c(seq(1,10,by=1),seq(500,800,length.out=10),seq(30,90,length.out=10), seq(5,19,length.out=10),seq(450,1080,length.out=10),seq(20,60,length.out=10), seq(2,15,length.out=10),seq(600,750,length.out=10),seq(80,25,length.out=10)))
plot<-ggplot(data,aes(x=Date,y=Data,color=as.factor(Station)))+
geom_line(size=1)+
facet_grid(Description~.,scales="free_y",switch="y")+
xlab("")+
ylab("")+
theme(panel.background=element_blank(),
panel.grid.major.y=element_line(color="grey80",
size=0.25),
panel.grid.major.x=element_blank(),
axis.line=element_line(color="black"),
strip.placement="outside",
strip.background=element_blank(),
legend.position="top",
legend.key=element_blank(),
legend.title=element_blank())
plot
plot.b<-ggplot_build(plot)
plot.g<-ggplot_gtable(plot.b)
data2npc <- function(x, panel = 1L, axis = "x") {
range <- plot.b$layout$panel_params[[panel]][[paste0(axis,".range")]]
scales::rescale(c(range, x), c(0,1))[-c(1,2)]
}
start <- sapply(as.Date("2018-10-10","%Y-%m-%d"), data2npc, panel=1, axis="x")
plot.g <- gtable_add_grob(plot.g, segmentsGrob(x0=start, x1=start, y0=0, y1=1, gp=gpar(lty=2)), t=7, b=13,l=7)
grid.newpage()
grid.draw(plot.g)
And new resulting plot