[R] Labeling Dates of different length on two in axis plot

[Ogbos Okike]

Dear Contributors,
I have two dataset of different lengths, each containing year, month,
day and counts.
After converting the date using as.Date function, I plotted the two
dateset on one graph. That was fine.

I am, however, having problems with the axis 1 where I am trying to
put the dates.
Since the two dates are not exactly the same, I stored the first date
as x1 and the second x2. x1 runs from 1953-01-02 to 2006-11-15 while
the range of x2 is between 1957-07-26 and 1994-07-17.
I tired a number of approaches but the one that seems to come close to
what I am looking for is: axis.Date(1, at=seq(min(x1), max(x1), by="50
mon"), format="%Y").

Unfortunately, it only labeled the axis up to 1994 even when I tried
to replace x1 with x2 in the code. Since one of the dates is up to
2006, I I wish to display the minimum (1953) and maximum  (2006) dates
and some possible intermediary dates.
I am always indebted to you.

Best wishes
Ogbos