NA response while downloading lists

I am trying to download Russell 2000 stocks(and other lists) for backtesting with dead stocks too.
I use Python Datastream API. I start from 1990 and get the list of constituents then download them.
For most of the lists I only get N/A so no stocks.
Only for a list: LFRUSS2L I get stocks but they are less than 2000 !
I attach my code.
Thanks Gabriel
The code I use:

...
mlist = set()
mmyy_list = []

for yea in range( 60, 122):
    for mo in range(1 , 13):
        yea2 = yea
        if yea2 > 99:
            yea2 -= 100
        stri = str(yea2).zfill(2) + str(mo).zfill(2)
        mmyy_list.append(stri)
print(' ***** STARTING ' + symb)

ds = dsws.Datastream(username=user, password=pw)

# call Datastream to get RICs list
rics_list = {}
for mmyy in mmyy_list:
    reque = symb + mmyy + '|L'
    try:
        dat = ds.get_data(tickers=reque, fields=['MNEM'], kind=0)
        # print(dat)
        # save rics list in python dict
        rics_list = dat['Value'].tolist()
...