I bought an M305 at the end of October, to use as a donor receiver for an IDF build. It was never fired in the original configuration. The bolt is numbered 24xx and has the circles on the underside exactly as those in the above pictures. It also shows a complete absence of tool marks and is the same black colour as Apple Tree's bolt. If the numbers are sequential (as I would assume), then this is indicative that the manufacturing process has changed at some point, IMO. The receiver shows tool marks typical of the other Norinco receivers, so I reckon that the receiver manufacturing is unchanged.
I think that anyone who has bought an M305 in the last two years should inspect the bolt on their rifle and at least be aware of the pattern of failures, the serial number, and the circular marks/black colour of the bolt. If the colour and markings are consistent, then that would be a very quick indication of a potential problem.
I have enough leftover parts to build another M14 if I can source another receiver, but there's no way my Norinco bolt is ever going to be more than a paperweight until there is some resolution on this.