How to enter a single case twice without increasing the total number of the cases in the dataset? My research is archaeological and I am looking at distribution of Roman lamps across time. Most of my lamps are coded into 50-year brackets within a single categorical variable (0-50 CE =1, 50-100 CE =2, 100-150 CE =3, 150-200 CE =4 and so forth). 
I, however, have a number of lamps that cannot be neatly dated/categorised as above. For instance, I have a lamp that I’ve dated to 50-150 CE. For various reasons, I have decided to enter that lamp 2 times – once 50-100 CE =2 and once 100-150 CE =3. If I, however, enter a single lamp twice, creating a new case for each date, then this will increase the total number of object entries I have (e.g. n=100 will rise to n=101).
Is there a way to enter a single case (lamp) twice without increasing the total number of the cases (lamps) I have entered into my SPSS dataset? is there something similar to a dummy case I could perhaps use? (I need it to run descriptive and chi-square analysis).
Thanks in advance
 A: I don't use SPSS much, but the problem is a neat one. I'll use Stata, below.
I'm not sure that you can do this while preserving the neat 50-year categories in a single variable. However, you can try entering the start and end years for each observations:
obs    start    end
1        0       50
2        0      100
3       50      100
4       50      150

You can derive duration, too.
obs    start    end    duration
1          0     50          50
2          0    100         100
3         50    100          50
4         50    150         100

Using these three, I can select particular categories. For example, if I wanted to count the number of lamps in 0-50 CE, I would
. generate mark=1 if start==0 and duration==50

obs    start    end    duration    mark
1          0     50          50       1
2          0    100         100       .
3         50    100          50       .
4         50    150         100       .

I also have the advantage of asking questions about lamps that span categories. For example, I want to know how many lamps were in existence at 75 CE
.generate mark2=1 if start<75 & end>75

obs    start    end    duration    mark    mark2
1          0     50          50       1        .
2          0    100         100       .        1
3         50    100          50       .        1
4         50    150         100       .        1

This technique has the added advantage of incorporating future information that better establishes the dating of a lamp. For example, say lamp 1 is re-analysed and dating techniques are now able to place it between 30 and 45 CE. You can simply adjust the start and end values of lamp 1
obs    start    end
1         30     45
2          0    100
3         50    100
4         50    150

