Different countries have different customs and so do different fields. This applies to the value of conference certificates. They are often just something that you can hang on your wall if you want to brag. Maybe if you get reimbursed for conference costs, someone would like a paper confirmation.
Independent of certificates, all authors have published (independent of certificates). In the US, graduate student admission committees trust claims about papers to be published because inventing a publication would be (in general) sanctioned with throwing a deceiving student out of the program. Besides, presumably a co-author would write one of the letter of reference.
Once the proceedings are in the printing stage and the electronic version available, any claim about publication is already verifiable. Google Scholar picks it up almost immediately. If LNCS refers to the Springer series, then, based on recent experience, Springer is very quick at processing the final versions of papers. Finally, most conferences have websites with lists of accepted papers that often appear within days of sending out acceptance letter. Once the program is finished, it usually gets published very quickly.
In conclusion, there are many simple ways to verify claims of published papers. There is a small window between the 'authors have received a letter of acceptance' and 'claims of authorship can be verified' that a certificate would not cover in any case. Thus, for admission purposes, certificates are useless.
Good luck with finding a good graduate program and do not worry about certificates.