If a router is actually experiencing dropped packets, in repeated traceroutes/plots it will generally fluctuate. It may be * * time, or * time *, or even ***, but the important thing to notice is the perceived source of the problem over the course of several plots.
That is, any hop which is actually dropping packets and experiencing packetloss will generally affect every subsequent hop in the trace.
Watch for ping spikes that are sustained across several hops (and are significant or exponential, rather than the expected 30-60ms hop for a geographical distance, i.e. virginia to texas or michigan to california, or overseas to usa) and packetloss which represents itself across one hop and every significant hop thereafter.
If it's a single hop or a few hops that show as blanks but everything after that hop is pinging fine, you're probably fine too.