The images in your "converted" LR CC catalog should still have the original Develop settings (Process Version 2003). When you change the Process Version on an image file to the newer Process Version 2012 LR will update the Basic panel settings to what it thinks most closely match. The resulting Basic panel settings are generally less than optimum.
When using or converting image files with PV2012 the best results are obtained with the Tone sliders at '0' (double-click on the word 'Tone' in the Basic panel). Then adjust the Tone controls from the top-down. Below is the procedure I use, which works well:
1. Set Exposure to correct the image midtone brightness ignoring the highlight and shadow areas for now. Setting Exposure slightly higher (+.25 to +.50 EV) than what looks correct for the midtones seems to work best with most images.
2. Leave Contrast at 0 for now. It’s usually better to adjust this after the first pass.
3. Adjust Highlights so that blown out areas are recovered and/or “fine tonal detail” is revealed.
4. Adjust Shadows to reveal fine detail in dark areas. For most normal images simply setting +Shadows the same as -Highlights (Example +50 and -50) works very well.
5. The Whites control sets the white clipping point, which you can see by holding down the ALT key as you move the slider. Adjust it to the point where you see clipping appear with the ALT key.
6. The Blacks control sets the black clipping point, which you can see by holding down the ALT key as you move the slider. Adjust it to the point where you see clipping appear with the ALT key. With very low contrast images such as a picture shot in foggy weather you may not want to use a lower setting (i.e. no Black clipping).
7. Now go back and adjust the Contrast control to establish the best midtone contrast. Ignore its effect on the overall image contrast. That is set by the Whites and Blacks clipping point controls.
8. Lastly touchup the Exposure control for the best midtone brightness.
9. If necessary “touch-up” the controls using the same top-down workflow.
You can also try using the Auto Tone button, but the results are unpredictable with many images.