FLC OF MDT DEPARTED CLRED ALT PRIOR TO GLIDESLOPE INTERCEPT WHILE FLYING ILS APCH FOR WHICH THEY HAD EARLIER DISCARDED APCH PLATES. UNUSUAL APCH IDENTIFICATION AND TERMINOLOGY ON THE CHART; NOT ADDRESSED BY THE PUBLISHER; CONTRIBUTED TO THE CONFUSION.

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I COMPLETED A COMMERCIAL CHART REVISION DATED 1/FRI/03 . THE PREVIOUS EVENING TAKING NOTE OF THE EFFECTIVE DATE OF 1/THU/03. ON APCH TO DFW ON 1/FRI/03; WE WERE GIVEN THE 'Y 36L ILS.' I RECALLED DURING THE REVISION THAT A NOTE ON THE CHART FOR THIS PARTICULAR APCH SAID 'PROC NOT IN DATABASE.' THUS; I DISCARDED THE CHART; MISTAKENLY THINKING THIS NOTE APPLIED TO US. NEITHER THE PLT FLYING NOR I HAD THE 'Y 36L ILS' APCH CHART. RATHER THAN ACCEPT ON FREQ EMBARRASSMENT; WE PRESSED ON; PLUGGING IN THE LOCALIZER FREQ FOR 'ILS 36L.' (111.9). LEVEL AT 3000 FT; THIN OVCST OF 2100 FT; 7 MILES VIS. WE BECAME CONFUSED WITH AN ARPT S OF DFW (IT ALSO HAD A N/S ALIGNMENT). BELIEVING HE WAS HIGH; THE PF STARTED TO DSND; LOSING 700 FT BEFORE REALIZING ERROR. HE THEN CLBED TO ORIGINAL ALT OF 3000 FT. AT SOME POINT; I ASKED TO CONFIRM THE FREQ FOR THE APCH. TWR REPLIED '110.55. IT LINES YOU UP WITH RWY 36R.' NO COMMENT WAS HEARD FROM TWR ABOUT OUR ALT. WE LANDED WITHOUT INCIDENT. WHAT CAUSED THIS WAS 1) DISCARDING THE APCH CHART AND 2) CONTINUING THE APCH (VIS WAS GOOD WITH A VERY THIN OVCST). LESSON ABOUT PREMATURELY DISCARDING CHARTS HAS MOST CERTAINLY BEEN LEARNED. WOULD LIKE TO SEE MORE INFO REGARDING THE PURPOSE OF 'Y ILS 36L' OR 'Z ILS 18L' APCHES. WHY THE 'Y' OR 'Z' DESIGNATION? CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: CALLBACK TO RPTR WAS COMPLETED 13 DAYS AFTER INITIAL REVIEW BY ANALYST. AT THIS DATE RPTR STATED THAT HE WAS STILL UNAWARE OF THE MEANING AND INTENT OF THE PHRASE 'PROC NOT IN DATABASE' ON THE APCH PLATES; NOR WITH THE IMPLICATIONS OF THE MODIFIERS 'Y' AND 'Z' IN THE PROC NAME. HE REITERATED THAT THE LACK OF INFO REGARDING THESE MATTERS LED BOTH HE AND HIS CAPT TO SIMPLY DISCARD THE PLATES AS UNUSABLE FOR THEIR OP.