When speaking on date codes you need to keep things in general terms because there always seems to be exceptions whenever someone lays down the law about cutoff dates, trends, "the norm", etc. Be careful what and who you believe on this subject because there is a TON of misinformation handed out on this site and elsewhere.
Various part date codes will vary in respect to the cars Scheduled Production Date on an individual part basis. Some are generally rather close to the SPD, while other parts may vary widely.
In your question you've left out a key ingrediant to helping you, your cars Scheduled Production Date, your VIN sequence is not very helpful in determining date codes on parts.
Post a photo of your cars fender tag or better, your broadcast sheet. Keep in mind that with any of your original parts that are missing you will never know for certain what the codes were or should be, at best you can use tips given here and some educated guesswork and you might get them close enough to be considered "possibly correct" or "acceptably correct" for your particular car.
If so the VIN # should read LM23P 
