A140828 pencil injector – pop off rating

My first post. Hope it is acceptable. Here is the background story ( as brief as I can be) I am helping a friend with injector trouble on his Case backhoe (580D CK). I pulled them and had him get them tested. Injectors 1 & 2 popped at 2800. #3 was solid plugged and #4 popped at 3200. This made perfect sense as my trouble shooting found that 1 & 2, when line was cracked made minimal difference in rpm. Line 3 made no difference but line 4 almost killed the engine when I cracked that line. I'm no expert at all, just been workin on my own junk a long time and have common sense. Looking online, I found a number of sources for injectors but they all seemed to be made in China (duh right?). I placed an ordered but then found it would take to long to get so my friend called an injector shop to the north of us and they drop shipped to us quickly. I did not ask about the brand as I respect this business. Injectors arrived and they were from China, dam. No numbers so I could not cross reference or compare to what the case manual listed but here is where I am most confounded. The manual lists several injector serial/part numbers with two different styles (double & single locknut / short and long tip - respectively) and pop off pressures of the three groupings listed. The nitty gritty of my delirium is that the number my friend took from one of his old injectors was supposedly A140828. The manual showed A140827 as a 2800lb injector and A149829 as a 3200lb injector... there was no A140828 number listed in any of the three groups of injector styles in the manual. It is Saturday tomorrow and I really wanted to put this machine back together for my friend however, I'm not sure of the pop off pressure of the new China injectors, and I am now concerned that if they happen to be 2800lb injectors, that the timing will be advance (he had some knocking that came and went I tested the engine under load), and thus may not produce full power (cylinder 4 with 3200lb injector was producing great power as evidenced by test). I do hope I made clear enough sense so that you all might appreciate my situation. I'm sure no matter what, that the engine will run much better with 4 uniformly performing injectors. Does anyone have knowledge of why there would be two different pop-off pressures listed in the book for this machine? Friend gave serial number as 207DT 5311053 (he said last number may have been an 8 instead of a 3). Wondering if my thinking on this is anywhere near the ballpark. Any thoughts would be interesting and appreciated. Tracktorman