Can you get the Lambda Locator achievement in multiple sessions in Half-Life 2?

Pretty much as per the question. Do you have to do this in one playthrough, or can you reload chapters and pick up the missing ones later?

Solution 1:

Yes (as noted by the Half Life Wikia) you can get them out of order if you miss some and need to go back for them. Unfortunately I don't think the achievement visibly allows you to track your progress, but it does take note if you've ever found one at all.

Solution 2:

On the Steam platform, you can do them in as many sittings as you like, and can also use the console to hop around to maps as needed to complete them.

You can ascertain which Lambda caches you are missing by the procedure documented here.

Basically you search your game library (found in one of your chosen install locations) called "gamestate.txt". Typically it is found in

  .../steamapps/common/Half-Life 2/hl2/gamestate.txt     or 
  .../steamapps/common/Half-Life 2 Update/hl2/gamestate.txt

Search the file for any lines containing the word "data", you are looking for

    {
            "id"            "86"
            "value"         "0"
            "data"          "0x00000FFFFFFFFFF7"
    ...

Note the ID = 86. That is the Lambda Locator achievement.

The large, 64-bit hex number there is the locations you have (and do not). It reads bitwise right to left, with (what numerous resources online describe as) location 1 being the least significant bit, and location 45 being the most significant (the first 5 hex digits will be 0x00001). Note in my example, location 45 shows as not discovered, which is a problem I'm having with Half-Life 2: Update actually. Also not discovered is location 4, noting the last digit of 0x7 .