There are several projects I have - one of them is comparing the various available satellite catalogs. The "default" official international satellite catalog is provided by the US Air Force - the Joint Space Operations Center (JSpOC). A long time ago I was an Orbital Analyst in a predecessor to that organization. The JSpOC provides a catalog that is adequate at best and I am hoping to contribute to the conversation about where that satellite catalog should end up. Another major catalog is the International Scientific Optical Network (ISON) which is maintained on a web page based in Russia.
One thing that should concern us is that the JSpOC satellite catalog does not release orbital elements for a number of satellites that have classified missions. To give them cover, they also do not release elements for their upper stages, sub-satellites deployed on those launches, etc. These have a variety of orbits - lower and higher above the Earth. There are a number of satellites that have low perigees that are in that group, these satellites will eventually reenter but there will be no alert about this reentry. People might be concerned by what they observe, for events that can be predicted.
There are currently 19 satellites that I watch, they have low perigees.
Satellites can seldom survive going down to 150 km, the ISS orbits at or above 400 km. Some of these satellites have higher (over 10,000 km) apogees and so the perigee can go up and down. But these where the perigee goes down to about 300 km should be watched closely.