Hi Hannah.
I didn't catch which printer you are using and that can effect your options. I hope you have one with a replaceable/reusable waste ink tank. I have experienced the same deterioration with a number of different Epson printers (from an R800 to a 7880).
My analysis is that if you get a good Nozzle check, like the first one you showed, but get one with gaps after you have printed an image, this indicates that there is a blockage that is slowing the ink flow to the head. A perfect nozzle check at startup is always reassuring but, especially if you are unsure of your printer's performance, or if you detect that the colours aren't printing quite right, it pays to do a nozzle check after printing an image to give confidence that the printer has been working properly throughout.
On a printer with cartridges that sit on the printer head my first advice is to remove the cartridges and find a syringe and a piece of plastic tube to fit over the piece that goes into the printer cartridge of the colours giving you trouble. Fit some absorbent paper under the printer head, fill the syringe with warm water and gently apply some pressure to the syringe plunger. If you can move about 5 ml of water through the head this should clear any blockage on that channel.
On printers where the ink cartridges feed the ink to the head via tubes, the place that I look for blockages are the ink buffers in the printer head.
Epson recommends that these buffers be replaced every two years on a printer doing a reasonable amount of work (they are quite vague) but the problem is that if pigment ink sits unused for a while the pigment particles can settle and coagulate or worse. Also, if you are using the printer a lot then comparably large amounts of ink are passing through these buffers which have a very fine mesh filter inside them. This filter can also block from ink particles that are filtered out because they are too big for the printer head nozzles.
The buffers are incorporated into the printer head mechanism. On some printers (the 7880 and 9880 are examples) the buffers are relatively easily replaced. On the 38nn series the easiest way to replace the buffers involves buying a part that includes the buffers, some electronics, the ink lines and the ink cartridge housing. I recommend buying an Epson Maintenance Manual if you want to undertake any of this sort of work. The maintenance manuals are extremely well documented and give step by step instructions on disassembly and reassembly. I can highly recommend them.
Cheers
Rob
