That's the way it was built, many boats of that era were. In fact, many boats did not come lifelines at all, it was a purchase option. or added by the owner. Some boats had removable lifeline stanchions... separate base and pole.
If you want to convert to double lifelines you can try drilling the holes, or simply replace the stanchions with two holed ones. Check Garhauer Marine dot com for good prices on lifeline stanchions. I replaced mine a few years back because a couple of the base welds were failing.
Safety wise. I dont think it makes that much difference, lifelines on old production boats were never that robust and you should never use them as an anchor for your pfd harness tether.