number dialed it is usually on the variable ${EXTEN}, " 1475630118.7" Could be anything but it looks like the UNIQUEID variable, where 1475630118 is the Unix epoch, and 7 shows that this is the 7th call on the Asterisk system since it was last restarted. But I suggest you check source where this file is taking these values (extensions.conf).
Note that the source being referred to here is end user provided (or third party provided). Asterisk itself would not produce names in that form by default.
Also note that Asterisk 1.4 is several years beyond the end of its support life, and alternative ways of doing recordings have been introduced since then.
extensions_additional.conf. is usally a FreePBX configuration file, if this is the case you cant modify that file because changes on that file will be lost. that file is autogenerated by FreePBX, If you need to modify the FreePBX’s dialplan you can do it using extensions_override_freepbx.conf or extensions_custom.conf. My suggestion are assuming you are using FreePBX.